During 1942, Trump became Secretary of the Microwave Committee, a sub-committee of the NDRC. The director of the Microwave Committee was Alfred Lee Loomis, the millionaire physicist, who decided to create a laboratory. He selected a site for it, chose a suitably discreet and ambiguous name for it and funded the construction, until the Federal administration was established. The new institution was the MIT Radiation Laboratory, or the "Rad Lab". The British were also researching radar, which they termed Radio Direction Finder (RDF), and had started much earlier. Their Tizard Mission to the US showed how much more sophisticated they were with some of the technologies, particularly the magnetron. The US decided to send a team to Britain to help coordinate the efforts of the two Allies. The unit was known as the "British Branch of the Radiation Laboratory" (BBRL) and operated as a department of Britain's Telecommunications Research Establishment (TRE) at Malvern, in Worcestershire. In 1943, as the technical aide in Division 14 of the NDRC, Trump reviewed and analyzed the papers of Dr. Nikola Tesla when Dr. Tesla died in a New York City hotel. The research was completed on behalf of the Alien property Custodian office in Washington DC. From February 1944 to the end of the war in Europe, Trump was the Director of the BBRL.[7] During this time, Trump also served in the Advisory Specialist Group on Radar, advising USAAF General Carl Spaatz on navigational radar, precision-bombing radar, and also defenses against the German radars found in their night-fighters and in their flak units. The systems included: Gee, Oboe, LORAN, H2X, MEW & SCR-584. Trump worked with all the most important British radar experts, including Sir Robert Watson-Watt, A.P. Rowe and Bernard Lovell. At the end of the war, Trump also had interviews with Germany's main radar technicians. Trump received recognition for his war-work from both the United States and the United Kingdom.[citation needed]

He returned to MIT to teach and direct research for three decades after the war. Trump died in Boston on February 21, 1985.[8]

The National Academy of Engineering described Trump as "a pioneer in the scientific, engineering and medical applications of high voltage machinery".[4] James Melcher, Trump's lab director, is quoted as saying: "John, over a period of three decades, would be approached by people of all sorts because he could make megavolt beams of ions and electrons – death rays. ... What did he do with it? Cancer research, sterilizing sludge out in Deer Island [a waste disposal facility], all sorts of wondrous things. He didn't touch the weapons stuff."[9]